Abstract

Receptors for 5-hydroxytryptamine (5-HT) are widely distributed over the mammalian peripheral nervous system (Wallis, 1981; Fozard, 1984). Those located on afferent neurones generally mediate excitatory actions of 5-HT, with neuronal inhibition being only rarely encountered (Paintal, 1973; Wallis, 1981; Roberts, 1984; Higashi and Nishi, 1982). Until recently it was unclear which receptor subtype mediates the stimulant action of 5-HT on primary afferent neurones, because such responses are refractory to blockade by the older, classical 5-HT receptor antagonists such as methysergide or cyproheptadine (Fozard, 1984). However, the recent discovery of new agonist and antagonist drugs with a high degree of selectivity for the different 5-HT receptor subtypes (Bradley et al., 1986; Richardson and Engel, 1986; Saxena et al., 1986) has stimulated renewed interest in this topic.